Laser-height adjustment device for a construction machine

ABSTRACT

A laser-regulating means for a construction machine ( 2 ) for adjusting the height of a height-adjustable machining tool ( 8 ) includes three laser measuring heads which are directed to three measuring points ( 50, 52, 54 ) being spaced from each other on a reference surface ( 60 ), and an evaluating means, which, from the output signals of the laser measuring heads and from the known geometric arrangement of the laser measuring heads as regards the machining tool ( 8 ), determines the height of the machining tool ( 8 ) relative to a reference surface ( 60 ) and, from this height and from a target height determines a control signal for a height-adjustment of the machining tool ( 8 ). The construction machine is a road finisher ( 2 ) with a height-adjustable plank ( 8 ) or a cold planer with a height-adjustable milling drum.

DESCRIPTION

[0001] The present invention relates to a laser-regulating means for aconstruction machine for adjusting the height of a height-adjustablemachining tool.

[0002] In the building trade, and, in particular, in undergroundengineering, various construction machines are employed to machineand/or generate large surfaces, such that the same comprise a desired,often approximately plane profile. In road construction, these machinesinclude, for example, a road finisher, or paver, a cold planer for roaduse, a “motor grader”, and others. The construction machines usemechanical or electronic regulating means to facilitate a quick andcost-efficient high-quality generation of a surface with a desiredprofile. In the following the problems involved will be brieflydiscussed by means of a road finisher and a cold planer.

[0003] Generally, a road finisher operates with a crawler track gear ona prepared underground, onto which is applied a road surface, or roadpaving, or tarmac, yet to be finished. On the rear side of the roadfinisher, seen from the direction of travel, a height-adjustable plankis provided, on the front side of which a supply of paving material ispiled up, which is distributed and tracked by means of a conveyor, whichensures that, on the front side of the plank, there is always asufficient, yet not too great amount of paving material kept in supply.The height of the rear edge of the plank as against the surface of theprepared underground, which may also be formed by a previously existingroad surface, establishes the thickness of the finished road surfacebefore the same is subsequently further compacted by means ofcompactors. The plank is held at a traction arm, which is mounted in aheight-adjustable manner around a traction point arranged in the centralarea of the road finisher, with the height of the plank being adjustablevia hydraulics.

[0004] In prior art road finishers, for controlling the height of theplank establishing the thickness of the paving to be finished, use is,for example, made of a mechanical scanning device guided beside the roadfinisher along a reference surface. Corresponding to a height of ascanning ski detected by means of an evaluating means, the plank will bere-adjusted in height.

[0005] The reference plane, along which the scanning ski is guided,depends on the current processing operation. Typically, the operatingwidth of a road finisher is less than the width of the road surface tobe finished. For establishing the height plane of the road surface to befinished use is commonly made of a taut steel cable as a referenceheight for a first track of the total road surface to be finished. Whenlaying the second track, which is to follow the first track without anydisplacement in height, the scanning ski is guided above the previouslyfinished track, which then forms the reference surface. With prior artroad finishers it is thus possible, through the use of a scanning ski,to use different objects as a reference plane, such as, for example, thetaut reference cables and/or the previously finished track of the roadsurface.

[0006] However, this prior art type of height-regulating the plankcomprises some system-related disadvantages. If, for example, whenfinishing the second track, a finished track of the road surface is usedas a reference plane for guiding the scanning ski, and if the firsttrack has a certain, undesired waviness, a second track will inevitablycomprise a structure with errors, which correspond to a reproduction ofthe errors of the road surface in the area scanned by the scanning ski.

[0007] The mechanical scanning by means of a scanning ski inevitablyfollows some sort of envelope curve over the respectively highest pointsof the reference surface. If, there is, for example, an undesiredobstacle in the form of a stone on the reference surface, the undesireddeflection of the scanning ski caused by this trouble spot results in acorresponding height error of the finished track of the road surface. Afurther problem is based on the mechanical sensitivity of the scanningski, which may be easily damaged not only due to careless operatingpersonnel, but also becomes quickly worn out during normal operation.

[0008] From the U.S. Pat. No. 4,961,173 of the applicant, a controlsensor for a construction machine for generating height-control signalsand direction-control signals by scanning a reference cable or guidecable is known. The prior art control sensor has a plurality ofultrasound transceivers which are arranged transversally to thedirection of motion of the construction machine and which are arrangedadjacent to each other, such that their lobes overlap in the measuringplane in which the guide cable or the reference cable is located.

[0009] The EP 0542297 B1 describes an alternative regulating means, inwhich at least three ultrasound sensors are mounted at the plankessentially in the direction of motion of the road finisher and spacedfrom each other, and in which an evaluating means uses the distancesignals of the ultrasound sensors for generating a height-control signalfor adjusting the plank. Among other things, this principle allows anaveraging of the surface in direction of travel and, in practice, leadsto satisfactory results. Yet, it has some decisive practicaldisadvantages. Since the sensors have to be arranged vertically abovethe respective measuring points on the floor, a stable constructionneeds to be built along the distance to be averaged in order to keep thesensors in position. For delivering good accuracy, also the ultrasoundsensors have to be mounted as close as possible (approximately 30 cm) tothe reference surface. Disadvantages of this ultrasound-regulating meansinclude the high construction requirements, the hindering of workersduring activities at or near the construction machine, and the danger ofmechanically damaging the sensors and the construction carrying the samein rough field conditions.

[0010] The EP 0547378 B1 describes an ultrasound regulating means for amobile planer. An evaluating means uses the signals of at least threeultrasound sensors to generate control signals for the gearheight-adjusting means depending on an adjustable target cutting depth.This apparatus provides the same disadvantages described above inconjunction with the road finisher.

[0011] Further, a laser-based regulating means for a road finisher isknown. A laser scans the profile of the unfinished surface beforeapplying the paving material and of the surface of the freshly appliedpaving material along a plane alongside the direction of motion of theroad finisher and vertical to the road surface in a multitude ofmeasuring points. From the thus obtained profile data, an evaluatingmeans generates a control signal for controlling the plank of the roadfinisher. The disadvantage of this system consists in the comparablycomplex and sensitive mechanics of the laser scanner used.

[0012] The DE 3827617A1 describes a scanning sensor, which enables atrack-like nominal plane recognition, for the purpose of which, forexample, curbstones may be used. A distance, which is pre-adjustableover the same, may serve to move the machining apparatus in a desiredplane-height relative to the thus generated reference plane and toautomatically align the same. The scanning sensor may be based on theuse of ultrasound, a laser beam or other optical scanning systems.

[0013] It is the object of the present invention to provide aconstructively simpler, mechanically more robust regulating means for aconstruction machine, which offers a higher degree of user friendlinessat the construction site, for adjusting the height of aheight-adjustable machining tool.

[0014] This object is achieved by a laser-regulating means in accordancewith claim 1.

[0015] The present invention provides a laser-regulating means for aconstruction machine for adjusting the height of a height-adjustablemachining tool, comprising a first laser measuring head, a second lasermeasuring head, and a third laser measuring head, which are arranged atthe construction machine, with the first laser measuring head and thesecond laser measuring head being arranged at a first angle to eachother, with the first laser measuring head and the third laser measuringhead being arranged at a second angle to each other, with the firstangle and the second angle being selected such that a first measuringpoint of the first laser measuring head, a second measuring point of thesecond laser measuring head, and a third measuring point of the thirdlaser measuring head are spaced from each other on a reference surface,with the first measuring point, the second measuring point, and thethird measuring point being essentially arranged behind each another inthe direction of motion of the construction machine, and an evaluatingmeans, which, depending on output signals of the first laser measuringhead, the second laser measuring head, and the third laser measuringhead, determines a first distance of the first laser measuring head fromthe reference surface, a second distance of the second laser measuringhead from the reference surface, and a third distance of the third lasermeasuring head from the reference surface, on the basis of thedetermined distances and the known geometric arrangement of the firstlaser measuring head, the second laser measuring head, and the thirdlaser measuring head relative to the machining tool, calculates theheight of the machining tool relative to the reference plane, and,depending on the calculated height and a target height, generates aheight-control signal for the machining tool.

[0016] An advantage of the inventive regulating means consists in thatthe arrangement of the laser measuring heads and the arrangement of themeasuring point on a reference surface are essentially independent ofeach other. On the one hand, therefore, the laser measuring heads may bemounted at a place, at or in the environment of the constructionmachine, where are no hindrance to certain jobs carried out or toworkers working there, and where they are safe from any damage, forexample, at a height of several meters. On the other hand, the positionof the measuring points on the reference surface is essentially freelyadjustable to the practical requirements.

[0017] The use of three laser measuring heads enables enhancing theregulating pcablerties of the laser-regulating means by recognizingartifacts using a simple plausibility control, the former, for example,resulting from objects on or holes in the reference surface and nothaving any impact on the regulation of the tool, as well as bycompensating for any waviness of the reference surface by means ofaveraging.

[0018] A preferred embodiment of the inventive laser-regulating meansfurther includes a fourth laser measuring head and a fifth lasermeasuring head which are arranged on the construction machine with athird angle and/or under a fourth angle as against the first lasermeasuring head, with the third angle and fourth angle being selectedsuch that the first measuring point, the second measuring point, thethird measuring point, a fourth measuring point of the fourth lasermeasuring head and the fifth measuring point of the fifth lasermeasuring head are spaced apart from each other on the reference surfaceand that the measuring points are located essentially behind each otherin the direction of motion of the construction machine, with theevaluating means calculating the height of the machining tool dependingon a fourth distance of the fourth laser measuring head as against thereference surface, a fifth distance of the fifth laser measuring head asagainst the reference surface and the known geometric arrangement of thefourth laser measuring head and fifth laser measuring head with respectto the machining tool.

[0019] Preferably, the laser-regulating means determines the differencesof two distances each and classifies those distances as valid, thedifference of which is smaller than a limiting value, or discards one ofthe determined distances as invalid and does not use the same forgenerating the height-control signal, if the distance involved rangesoutside a predetermined range. The predetermined range may be specifiedby a predetermined distance above/below a plane, with the plane beingspecified by the remaining distances.

[0020] Preferably, the evaluating means forms the mean value of thedetermined and, if necessary, not-discarded distances.

[0021] Preferably, the laser measuring heads are further adjacent toeach other in spatial proximity, arranged essentially behind each otherin the direction of motion and arranged essentially at equal distancesto the machining tool. In this case, the total laser-regulating meansmay be arranged in a compact housing, such that no mechanical orelectrical connection to remotely arranged sensors is required. As aresult of this, disadvantages in connection with interrupted or damagedsignal lines can be avoided, which occur in prior art constructionmachines owing to the required arrangement of the ultrasound sensors.

[0022] An advantage of the inventive laser-regulating means consists inthat it does not contain any moveable or moved parts, such that the sameare especially robust, less error-prone and easy to implement in termsof construction, manufacture, assembly, and maintenance. The specialrobustness is especially important under the conditions at aconstruction machine (vibrations, a very high working temperature range,humidity, etc.).

[0023] The inventive laser-regulating means is, for example, attached toa road finisher or to a cold planer.

[0024] Preferably, one of the laser measuring heads is aligned with thepertaining measuring point and the machining tool

[0025] Preferred embodiments of the inventive laser-regulating meanswill be explained in detail below with reference to the attacheddrawings, in which:

[0026]FIG. 1 shows a road finisher with the inventive laser-regulatingmeans in accordance with a first embodiment;

[0027]FIG. 2 shows a schematic plan view of the road finisher from FIG.1;

[0028]FIG. 3 shows a block diagram of the inventive laser-regulatingmeans in accordance with a second embodiment; and

[0029]FIG. 4 shows a cold planer with the laser-regulating means inaccordance with the first embodiment.

[0030]FIG. 1 shows a road finisher 2 having a crawler track gear 4 on aprepared underground 6. At the rear end of the road finisher 2 opposingthe driving direction, a height-adjustable plank 8 is arranged, which ismounted at a traction point 12 at the road finisher 2 by means of atraction arm 10. In front of the plank 8, there is a supply 14 of pavingmaterial kept essentially constant across the total width area of theplank 8 by a corresponding known regulation of the speed of a screw-likeconveyor means 16.

[0031] The plank 8 floats on the paving material of a road surface 18 tobe finished. The thickness of the road surface 18 to be finished priorto its final compaction by road compactors will be effected byregulating the height-position of the rear edge 20 of the plank 8. Thisheight-regulation is induced by changing the blade angle of the plank 8and is typically effected by controlling setting cylinders engaging intothe front end of the traction arms 10.

[0032] The previously described road finisher 2 is in accordance withthe road finishers in accordance with the state of the art such that, inconsideration of expert knowledge on the present technical field, it isnot necessary to go into a detailed description.

[0033] The road finisher 2 comprises a laser-regulating means inaccordance with the present invention which is attached in a housing 30via a mounting 32 at the traction arm 10. In the shown embodiment, thelaser-regulating means includes three laser measuring heads not shown inFIG. 1, which direct three laser beams 40, 42 and 44 to three measuringpoints, 50, 52 and 54 on a reference surface 60 beside, in front ofand/or behind the road finisher. As a result, the central lasermeasuring head is arranged vertically above the rear edge 20 of plank 8,such that the pertaining measuring point 52 lies on a straight line withthe rear edge 20 of the plank 8. The first laser beam 40 and the secondlaser beam 42 include a first angle 70, the first laser beam 40 and thethird laser beam 44 include a second angle 72. The reference surfacemay, for example, be established by an existing or just finished trackof the road surface, an already finished kerb strip of the road or anyother suitable surface.

[0034]FIG. 2 shows a schematic plan view of the road finisher 2 fromFIG. 1. The laser beams 40, 42, and 44, respectively, of the lasermeasuring heads in housing 30, which are not shown, are directed tomeasuring points 50, 52, and 54, respectively. The first measuring point50 and the second measuring point 52 lie on a reference surface 60,which is situated on the edge of the prepared underground 6 beingprovided with a road surface 18 while the road finisher is moving to theright. The third measuring point 54 lies on the edge of the finishedroad surface 18 and on a straight line with the first measuring point 50and second measuring point 52. Using several laser beams 40, 42, 44 ofseveral laser measuring heads enables a flexible arrangement of themeasuring points 50, 52, 54, which is adapted to the conditions andrequirements of the respective application field.

[0035] In FIG. 3, an embodiment of the laser-regulating means is shownwhich, in contrast to the embodiment shown in FIG. 1, includes fivelaser measuring heads 80, 82, 84, 86, 88 each having one functionallyrelated lens 90, 92, 94, 96, and 98, respectively. The laser measuringheads 80, 82, 84, 86, 88 emit laser beams 40, 42, 44, 106, 107, whichare directed to the respectively pertaining measuring points. Thelaser-regulating means further includes a number of transceiver circuits110, 112, 114, 116, 118 corresponding to the number of laser measuringheads 80, 82, 84, 86, 88. These transceiver circuits 110, 112, 114, 116,118 are in a respective electrical signal-connection to respectively oneof the laser measuring heads 80, 82, 84, 86, 88. The transceivercircuits 110, 112, 114, 116, 118 are further in an electricalsignal-connection to an evaluating means 120, which, for example, maycomprise a microcomputer. As is shown in FIG. 3, each of the transceivercircuits is connected to the evaluating means via two signal lines, withsignals being sent to the transceiver circuit via one line and signalsbeing received from the transceiver circuit via the other line, as isshown in FIG. 3 by the arrows associated with the lines. Via aninterface 122 and a first terminal 124, the evaluating means 120 isconnected to a non-illustrated apparatus for controlling the abovementioned setting cylinders attacking the front ends of the tractionarms 10 in order to influence the height position of the rear edge 20 ofthe plank and, thus, the thickness of the road surface 18 to befinished. The connection between the evaluating means 120 and theinterface 122 is schematically shown by the arrow 125 in FIG. 3. Via asecond terminal 126, the evaluating means 120 is connected to anon-illustrated apparatus, where a user may first set a target value forthe height-adjustment of the plank. Via a non-illustrated terminal, themembers of the laser-regulating means are supplied with electrical powerby a non-illustrated power source.

[0036] Each laser measuring head 80, 82, 84, 86, and 88, respectively,may be integrated with the respectively pertaining transceiver circuit110, 112, 114, 116, and 118, respectively, in a component (asillustrated) and/or with the pertaining lens 90, 92, 94, 96, and 96,respectively. The transceiver circuit 110, 112, 114, 116, and 118,respectively, the laser measuring head 80, 82, 84, 86, and 88,respectively, and the lens 90, 92, 94, 96 and 98, respectively,cooperate to determine the distance of the laser measuring head 80, 82,84, 86, and 88, respectively, from the respective measuring point on thereference surface 60 using the running time of the laser beam 40, 42,44, 106, and 107, respectively, from the time of its emission by thelaser measuring head 80, 82, 84, 86 and 88, respectively, to the time ofreceiving the laser light reflected from the reference surface 60 in thepertaining measuring points by the measuring head 80, 82, 84, 86, and88, respectively, and to send an electrical signal corresponding to thisdistance to the evaluating means 120. From the thus determined distanceof the laser measuring head 80, 82, 84, 86, and 88, respectively, andfrom its known geometric arrangement, the evaluating means 120calculates its distance from the reference surface.

[0037] The classification of functionalities shown in FIG. 3 within thelaser height regulating means merely represents an embodiment and may bevaried, for example, by integrating various illustrated components in acomponent. Further, the laser height regulating means may comprisefurther, not-illustrated interfaces for exchanging data with otherapparatuses, for example, other control and regulating apparatuses ofthe construction machine 2, with a central computer of the constructionmachine 2 or with an external computer for performing error diagnostics.

[0038] Depending on the respective special area of application of thelaser-regulating means and the conditions and circumstances related tothe same, the laser measuring heads 80, 82, 84, 86, 88, or the laserbeams 40, 42, 44, 106, 107 emitted by the same, are spatially alignedsuch, that the respective measuring points are spaced from each other asfar as possible, that is, that, for example, the first angle 17 betweenthe first laser beam 40 and the second laser beam 42, and the secondangle 72 between the first laser beam 40 and the third laser beam 44 arechosen as great as possible.

[0039] From the distances of the laser measuring heads 80, 82, 84, 86,88 as against reference surface 60 and the known geometric arrangementof the laser measuring heads 80, 82, 84, 86, 88 with respect to theplank 8, the evaluating means 120 determines the height of the plank 8as against the reference surface 60. From this height of the plank 8 asagainst the reference surface 60 as well as from a target height, whichcan be adjusted at the above-mentioned, not-illustrated apparatusconnected to the evaluating means 120 via the terminal 122, theevaluating means 120 determines a height-control signal for the plank 8.At the road finisher 2, this height-control signal serves forcontrolling the setting cylinders for adjusting the front tractionpoints 12 of the traction arms 10 of the plank 8.

[0040] In the following, preferred further processings of the detectedsignals from the laser measuring heads 80, 82, 84, 86, 88 by theevaluating means 120 for generating the height-control signal will bedescribed.

[0041] From the distances of the laser measuring heads 80, 82, 84, 86,88 as against the reference surface 60, which have been determined fromthe output signals of the laser measuring heads 80, 82, 84, 86, 88, theevaluating means 120 forms a mean value to determine the height of theplank 8 as against the reference surface 60. By means of averaging, theinfluence of a waviness of the reference surface 60 onto theheight-control signal is reduced and, thus, a better evenness, orsmoothness, of the just finished road surface 18 will be achieved. Thisaveraging functions the better, the more laser measuring heads 80, 82,84, 86, 88 or measuring points 50, 52, 54, 108, 109 are present on thereference surface 60 and the further the measuring points 50, 52, 54,108, 109 are spaced from each other on the reference surface 60.

[0042] Further, the evaluating means 120 may be implemented such thatthe evaluating means 120 discards a distance of a laser measuring head80, 82, 84, 86, 88 from the reference surface 60 as invalid and does notuse the same for generating the height-control signal, if the distanceinvolved lies outside a predetermined range. As a result, it ispossible, for example, to suppress the undesired transmission of variouserrors of the reference surface 60 to the road surface 18 to befinished. The predetermined range may be defined by a lower limitingvalue and an upper limiting value for the distance of a laser measuringhead 80, 82, 84, 86, 88 from the reference surface 60. The errors of thereference surface 60 include, for example, holes, stones or otherobjects lying on the reference surface 60, and the influence of whichonto the height-regulation of the plank 8 is mitigated, but noteliminated by the above-described averaging. The upper limiting valueand the lower limiting value are selected such that a waviness of thereference surface 60 is still within the range defined by the upperlimiting value and the lower limiting value in order not to discard toomany measuring points 50, 52, 54, 108, 109 as invalid and such that themost objects and holes on or in the reference surface 60 or thedistances generated by these ranges are outside the range in order notto have any influence on the height regulation of the plank 8. Theprecise values of both limiting values are dependent on the respectivecircumstance, for example, on the quality of the reference surface 60 ora longitudinal curvature of the reference surface 60 or the road surface18 to be finished as well as on the spatial arrangement of the measuringpoint 50, 52, 54, and, during use, may be manually or automaticallyadapted to the respective circumstances.

[0043] The just described range, outside of which one of the determineddistances may be discarded or is not used for generating theheight-control signal, may be specified in a laser height-regulatingmeans having at least three laser measuring heads 80, 82, 84, 86, 88 bya range above/below the plane which is defined by the remainingdistances. As a result, even in the case of a longitudinal curvature ofthe reference surface 60, the transfer of which to the road surface 18to be finished is desired, a small predetermined range is adjusted,within which distances may be classified as valid and are not discarded.

[0044] In a further embodiment, instead of the limiting values or theremaining distances, the difference between two distances each isdetermined, and those distances are discarded as invalid and not usedfor generating the height-control signal, the differences of whichexceed a predetermined limiting value as regards the distances of theother laser measuring heads 80, 82, 84, 86, 88 relative to the referencesurface 60. Thereby, errors at the reference surface 60 are alsoidentified and their influence on the height-control signal iseliminated.

[0045] The advantage of the laser measuring heads 80, 82, 84, 86, 88 asagainst conventional approaches using ultrasound measuring headsconsists in that, in contrast to ultrasound measuring heads, no verticalirradiation on the reference surface 60 and no small distance to thesame is required. Under normal circumstances, that is, in case of a nottoo strongly reflective reference surface 60, the laser measuring heads80, 82, 84, 86, 88 may also be used at great angles to the perpendicularand at a great distance to the reference surface 60. Therefore, it ispossible to arrange all laser measuring heads 80, 82, 84, 86, 88 largelyindependent of the arrangement of the pertaining measuring points on thereference surface 60. Especially, as is shown in FIG. 3, all lasermeasuring heads 80, 82, 84, 86, 88 may be arranged together with theevaluating means 120 and the interface 122 in a common housing 30, whichis mounted at the road finisher 2 at a height against the road whichessentially corresponds to the height of the road finisher 2. As aresult, the mechanical-constructive requirements for mounting theregulating means are significantly reduced. Further, the risk ofdamaging the regulating means in rough field conditions as well as theprobability of preventing construction site workers from performingactivities at the road finisher 2 and in the immediate vicinity of thesame is diminished.

[0046] Further, the laser measuring heads 80, 82, 84, 86, 88, which maybe adjusted in their spatial orientation as needed, but which areimmovable during operation, avoid the disadvantages of a laser scannerbeing moveable during operation and comprising a sensitive mechanic. Bycompletely dispensing with moveable parts, especially under the extremeconditions at a construction machine 2 (vibrations, very large workingtemperature range, humidity, etc.), reduced error-proneness, lowerfailure times, longer service life, and better efficiency are possible.

[0047] The road finisher 2 specified in the previous embodiments, isonly an example for a construction machine where the laser-regulatingmeans may be used to regulate the height of a height-adjustablemachining tool, such that the finished surface comprises a desiredprofile. A further example is the cold planer 200 illustrated in FIG. 4having a front gear 202 and a rear gear 204, at least one of which isadjustable in height. The machining tool is in this case a milling drum206, the height of which, and thus also the “cutting depth”, may beadjusted as against a not machined track 208 and a machined track 210,by adjusting the height-adjustable gear 202 or 204 or, if applicable, byadjusting the height of at least one of the height-adjustable gears 202,204. In the cold planer 200, the laser-regulating means alreadydescribed by means of FIG. 1 is mounted via the mounting 32 in thehousing. As a result, one of the laser measuring heads is aligned withthe pertaining measuring point and the axis of the milling drum (206).The height-control signal generated by the laser-regulating meanscontrols the height-adjustment of the gear 202, 204.

[0048] Further, the use of the laser-regulating means in accordance withthe present invention is possible with each construction machine whichchanges the profile of a surface, i. e. which removes or applies layers,to obtain a desired profile and, in the process, references to areference surface. Under certain circumstances, this may include abulldozer, a so-called motor grader etc.

1. Laser-regulating means for a construction machine (2; 200) foradjusting the height of a height-adjustable machining tool (8; 206),comprising a first laser measuring head (80), a second laser measuringhead (82), and a third laser measuring head (84), which are arranged atthe construction machine (2; 200), with the first laser measuring head(80) and the second laser measuring head (82) being arranged at a firstangle (70) to each other, with the first laser measuring head (80) andthe third laser measuring head (84) being arranged at a second angle(72) to each other, with the first angle (70) and the second angle (72)being selected such that a first measuring point (50) of the first lasermeasuring head (80), a second measuring point (52) of the second lasermeasuring head (82), and a third measuring point (54) of the third lasermeasuring head (84) are spaced from each other on a reference surface(60), with the first measuring point (50), the second measuring point(52), and the third measuring point (54) being arranged essentiallybehind each other in the direction of motion of the construction machine(29); and an evaluating means (120), which, depending on output signalsof the first laser measuring head (80), the second laser measuring head(82), and the third laser measuring head (84), determines a firstdistance of the first laser measuring head (80) from the referencesurface (60), a second distance of the second laser measuring head (82)from the reference surface (60), and a third distance of the third lasermeasuring head (84) from the reference surface (60), on the basis of thedetermined distances and the known geometric arrangement of the firstlaser measuring head (80), the second laser measuring head (82), and thethird laser measuring head (84) relative to the machining tool (8; 206),calculates the height of the machining tool (8; 206) relative to thereference plane (60) and, depending on the calculated height and atarget height, generates a height-control signal for the machining tool(8; 206).
 2. Laser-regulating means in accordance with claim 1,including a fourth laser measuring head (86) and a fifth laser measuringhead (88), with the fourth laser measuring head (86) being arranged atthe construction machine (2; 200) at a third angle relative to the firstlaser measuring head (80), with the fifth laser measuring head (88)being arranged at the construction machine (2; 200) at a fourth anglerelative to the first laser measuring head, with the third angle and thefourth angle being selected such that the first measuring point (50),the second measuring point (52), the third measuring point (54), afourth measuring point of the fourth laser measuring head (86), and afifth measuring point of the fifth laser measuring head (88) beingspaced from each other on the reference surface (60) and that the first(50), second (52), third (54), fourth and fifth measuring point lieessentially behind each other in the direction of motion of theconstruction machine (2; 200), with the evaluating means (120) furthercalculating the height of the machining tool (8; 206) depending on afourth distance of the fourth laser measuring head (86) relative to thereference surface (60), a fifth distance of the fifth laser measuringhead (88) relative to the reference surface (60), and the knowngeometric arrangement of the fourth laser measuring head (86) and thefifth laser measuring head (88) with respect to the machining tool (8;206).
 3. Laser-regulating means in accordance with claim 2, wherein theevaluating means (120) determines the differences of two distances each,and classifies those distances as valid, the differences of which aresmaller than a limiting value.
 4. Laser-regulating means in accordancewith claim 1 or 2, wherein the evaluating means (120) discards one ofthe determined distances as invalid and does not use the same forgenerating the height-control signal, if the respective distance liesoutside a predetermined range.
 5. Laser-regulating means in accordancewith claim 4, wherein the predetermined range is specified by apredetermined distance above/below a plane, with the plane beingspecified by the remaining distances.
 6. Laser-regulating means inaccordance with one of claims 1 to 5, wherein the evaluating means (120)averages the determined distances.
 7. Laser-regulating means inaccordance with one of claims 1 to 6, wherein the laser measuring heads(80, 82, 84, 86, 88) are adjacent to each other in spatial proximity,and are arranged essentially behind each other in the direction ofmotion and essentially at equal distances to the machining tool (8;206).
 8. Laser-regulating means in accordance with one of the precedingclaims, wherein one of the laser measuring heads (80, 82, 84, 86, 88) isaligned with the pertaining measuring point (50, 52, 55) and themachining tool (8; 206).
 9. Laser-regulating means in accordance withone of claims 1 to 7, wherein the construction machine is a roadfinisher (2), and the machining tool is a plank (8), which is connectedto the road finisher (2) via a traction arm (10), with the lasermeasuring heads (80, 82, 84, 86, 88) being mounted via a mounting (32)to the traction arm (10) in a common housing (30), with theheight-control signal generated by the evaluating means (120) causing anadjustment of a traction point (12) of the traction arm (10) of theplank (8).
 10. Laser-regulating means in accordance with one of claims 1to 7, wherein the construction machine is a cold planer (200) having afront (202) and a rear gear (204), at least one of which isheight-adjustable, and wherein the machining tool is a mill (206), withthe laser measuring heads (80, 82, 84, 86, 88) being mounted (200) in acommon housing (30) via a mounting (104) to the cold planer (200), withthe height-control signal generated by the evaluating means (120)causing a height-adjustment of the front (202) and/or rear gear (204).11. Laser-regulating means in accordance with claim 9, wherein one ofthe laser measuring heads (80, 82, 84, 86, 88) being aligned with thepertaining measuring point (50, 52, 55) and the rear edge (20) of theplank (8).
 12. Laser-regulating means in accordance with claim 10,wherein one of the laser measuring heads (80, 82, 84, 86, 88) is alignedwith the pertaining measuring point (50, 52, 55) and the axis of themilling drum (206).